THS4521 Datasheet, PDF (23/43 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521
THS4522
THS4524
www.ti.com.................................................................................................................................................... SBOS458B – DECEMBER 2008 – REVISED MAY 2009
Distortion
The circuit shown in Figure 54 is used to measure
harmonic and intermodulation distortion of the
amplifier.
An HP signal generator is used as the signal source
and the output is measured with a Rhode and
Schwarz spectrum analyzer. The output impedance
of the HP signal generator is ac-coupled and is 50 Ω.
R_IT and R_G are chosen to impedance match to 50 Ω
and maintain the proper gain. To balance the
amplifier, a 0.22-µF capacitor and 49.9-Ω resistor to
ground are inserted across R_IT on the alternate input.
A low-pass filter is inserted in series with the input to
reduce harmonics generated at the signal source.
The level of the fundamental is measured and then a
high-pass filter is inserted at the output to reduce the
fundamental so it does not generate distortion in the
input of the spectrum analyzer.
The transformer used in the output to convert the
signal from differential to single-ended is an
ADT1–1WT. It limits the frequency response of the
circuit so that measurements cannot be made below
approximately 1 MHz.
Slew Rate, Transient Response, Settling
Time, Output Impedance, Overdrive, Output
Voltage, and Turn-On/Turn-Off Time
The circuit shown in Figure 55 is used to measure
slew rate, transient response, settling time, output
impedance, overdrive recovery, output voltage swing,
and ampliifer turn-on/turn-off time. Turn-on and
turn-off time are measured with the same circuit
modified for 50-Ω input impedance on the PD input
by replacing the 0.22-µF capacitor with a 49.9-Ω
resistor. For output impedance, the signal is injected
at V_OUT with V_IN open; the drop across the 2x 49.9-Ω
resistors is then used to calculate the impedance
seen looking into the amplifier output.
V_IN+
From
50-W
Source
Open
Installed to
Balance
Amplifier
49.9 W
R_G
R_IT
PD
0.22 mF
R_G
R_IT
1 kW
V_S+
THS452x
V_OCM
V_S-
1 kW
49.9 W
49.9 W
V_OUT-
V_OUT+
Open
0.22 mF
To Oscilloscope
with 50-W Input
V_IN+
From
50-W
Source
Open
Installed to
Balance
Amplifier
0.22 mF
49.9 W
R_G
R_IT
R_F
V_S+
PD
0.22 mF
R_G
R_IT
THS452x
V_OCM
V_S-
R_F
R_O
1:1
R_O
R_OT
Open
0.22 mF
V_{OUT To 50-W}
Test
Equipment
Figure 55. Slew Rate, Transient Response,
Settling Time, Output Impedance, Overdrive
Recovery, V_OUT Swing, and Turn-On/Turn-Off Test
Circuit
Figure 54. Distortion Test Circuit
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